/*
 * Copyright (C) 2019 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.graph;

import java.util.AbstractSet;
import java.util.Set;
import javax.annotation.CheckForNull;

/**
 * Abstract base class for an incident edges set that allows different implementations of {@link
 * AbstractSet#iterator()}.
 */
@ElementTypesAreNonnullByDefault
abstract class IncidentEdgeSet<N> extends AbstractSet<EndpointPair<N>>
{
    final N node;
    final BaseGraph<N> graph;

    IncidentEdgeSet(BaseGraph<N> graph, N node)
    {
        this.graph = graph;
        this.node = node;
    }

    @Override
    public boolean remove(@CheckForNull Object o)
    {
        throw new UnsupportedOperationException();
    }

    @Override
    public int size()
    {
        if (graph.isDirected())
        {
            return graph.inDegree(node)
                    + graph.outDegree(node)
                    - (graph.successors(node).contains(node) ? 1 : 0);
        }
        else
        {
            return graph.adjacentNodes(node).size();
        }
    }

    @Override
    public boolean contains(@CheckForNull Object obj)
    {
        if (!(obj instanceof EndpointPair))
        {
            return false;
        }
        EndpointPair<?> endpointPair = (EndpointPair<?>) obj;

        if (graph.isDirected())
        {
            if (!endpointPair.isOrdered())
            {
                return false;
            }

            Object source = endpointPair.source();
            Object target = endpointPair.target();
            return (node.equals(source) && graph.successors(node).contains(target))
                    || (node.equals(target) && graph.predecessors(node).contains(source));
        }
        else
        {
            if (endpointPair.isOrdered())
            {
                return false;
            }
            Set<N> adjacent = graph.adjacentNodes(node);
            Object nodeU = endpointPair.nodeU();
            Object nodeV = endpointPair.nodeV();

            return (node.equals(nodeV) && adjacent.contains(nodeU))
                    || (node.equals(nodeU) && adjacent.contains(nodeV));
        }
    }
}
